In environments illuminated by artificial light sources, lighting management becomes increasingly important. In general, the use of solid state light sources, such as light emitting diodes, allows tuning the colour of the emitted light. It is generally desirable to be able to detect, e.g., the colour point and the colour rendering index of the light in the light source environment, as well as other properties of the light emitted from the light sources over a portion of the electromagnetic spectrum in order to control and adjust preferred light settings or to create dynamic lighting atmospheres. Moreover, it is preferable that such detection can be performed in an unobtrusive manner. In addition, it is desirable to be able to determine properties, such as those above, of light incident on certain positions in the lighting environment, such as an artificially lighted room. Thus, not only the flux, but also spectral information of the light sources is of interest. It would therefore be desirable to have an inexpensive, unobtrusive, and easily manufactured device capable of such detection.
A drawback with known spectral detectors is that they generally require auxiliary optical components which require alignment and space, and thus, are expensive and bulky, and can generally not be arranged unobtrusively at the desired location to perform spectral detection. A further drawback with known spectral detectors is that they are not capable of measuring characteristics of light, such as spectral information, as a function of the angle of incidence of the incident light without actually moving the spectral detector and/or a fiber coupled to the spectral detector.
Documents U.S. Pat. No. 5,762,823A and U.S. Pat. No. 5,798,057A disclose a method for manufacturing a switchable cholesteric filter comprising a mixture of polymerizable liquid-crystalline molecules provided between two substantially parallel substrates which are each provided with an electrode.